Rise of the Amniotes

The last common ancestor of Frith's modern reptiles and mammals lived at about this time.

The damp canyons of Frith began to go into a slow period of drying over the previous thirty million years before this date. The early tetrapods either died out, or gave rise to the amniote lineage. Amniotes are capable of bearing young on land and don't need to live an amphibious lifestyle. This evolutionary milestone would allow the relatively dry planet of Frith to teem with vertebrate life. Amphibians, meanwhile, would fade into ecological irrelevance and soon pass out of the fossil record.